In 2014 ConocoPhillips drilled the first of five deviated wells in DeWitt County, Texas, in order to sample the rock volume adjacent to a horizontal Eagle Ford producer prior to and immediately following hydraulic stimulation. The design, execution and results of the pilot will be described, with particular emphasis on the data acquisition program, which included core, image log, microseismic, DTS/DAS, and pressure data. The observed reservoir state preceding and following hydraulic fracturing will be discussed from an integrated perspective, emphasizing geologic, geophysical, reservoir engineering and completions related observations.

Introduction

The notion that hydraulic fractures in the subsurface are complex is not new (Mahrer et al., 1996, Mahrer, 1999, Cipolla et al., 2008). Fracture complexity has been proposed as one of the causes of high treating pressures and several studies have sampled complex hydraulic fractures. The most notable of these are hydraulic fracture core-through projects (Warpinski et al., 1993, Fast et al., 1994, Branagan et al. 1996) and hydraulic fracture mine back endeavors (Warpinski and Teufel, 1987, Warpinski 1991). In these studies, multiple hydraulic fractures were encountered close to each other and fracture deflections and branching at geological heterogeneities, such as natural fractures and bedding surfaces, were described. The observations from mine back data and hydraulically fractured vertical wells indicate that simple bi-wing fractures are not the norm in nature. By extension, this is likely the case for multi-stage horizontal wells completed in shale. Shales are more mechanically anisotropic than the sandstones previously studied and thus should be more likely to develop complex fracturing. With the maturation of microseismic imaging, the premise of complex fracturing has been reinforced (Walker et al., 1998, Fisher et al., 2002, Maxwell et al. 2002, Cipolla et al. 2008). In these, and other published case histories, microseismic event maps generally reflect a diffuse cloud that is typically interpreted as the result of fracture complexity.